1. Field of the Invention
The present invention relates to a scroll type compressor, and more specifically, to improvements in the structure of a counterweight and a drive bush in the scroll type compressor.
2. Description of the Background Art
Publication of Unexamined Japanese Utility Model Application No. 57-83291 (1982) discloses a scroll type compressor to which the present invention pertains. According to the conventional compressor, there are provided two inter fitting scroll members each having an end plate and an involute spiral element, one scroll member being orbitable relative to the other stationary member. The scroll members are angularly offset at 180.degree. to form line contacts between the interfitting spiral elements, thereby defining a fluid pocket or a fluid working chamber of the compressor. A drive shaft is rotatably supported in the compressor housing via a bearing, and has a crank pin disposed eccentrically and projecting axially inward from the inner end surface of the drive shaft.
The crank pin is disposed on top of a drive bush, which in turn supports the orbiting scroll member by means of a bearing. The drive bush is adapted to cooperate with an anti-spin mechanism in order to convert the rotational motion of the drive shaft into the orbital motion of the orbiting scroll member. At the same time, the bush and anti-spin mechanism prevent the orbiting scroll member from rotating on its own axis. Additionally, a counterweight for dynamically balancing the orbital motion of the orbiting scroll member is installed on the crank pin between the drive bush and the drive shaft end, and revolves together with the drive bush.
Fluid or refrigerant gas is drawn into the compressor through an inlet in the compressor housing, and is taken into the fluid pocket. The fluid or gas is next compressed when the pocket both moves toward the center of the scroll members while undergoing a reduction in it's volume. The compressed refrigerant gas is finally discharged through a discharge port formed at the center of the end plate of the stationary scroll member.
In the conventional compressor, the counterweight is connected to the drive bush by means of a rivet which is close fit through holes formed in the counterweight and the drive bush. One end of the rivet, remote from the drive bush, fits loosely into a hole formed in the drive shaft end. The loose fit results in a small clearance between the hole and accompanying rivet end which permits the drive bush to rotate with the counterweight about the crank pin only for a limited angular distance. This limited rotational movement of the drive bush about the pin allows the orbiting scroll member to compensate for possible wear or machining inaccuracies introduced in the interfitting involute surfaces of the spiral elements. Consequently, the stationary and orbiting scrolls can maintain an optimal positional relationship between themselves.
Unfortunately, due to the fact that the rivet end is loosely fit in the drive shaft end, it is subject to impact shock, torque and other rotational forces transmitted from the drive shaft to the drive bush, or vise versa, when compressor operation is started or stopped. These forces result in a shearing force being applied to the rivet. Repeated application of such forces may cause the rivet to deform or even break.